Beam processing apparatus

ABSTRACT

A beam processing apparatus comprises a workpiece holder ( 20 ) for holding a workpiece (X), a plasma generator for generating a plasma in a vacuum chamber ( 3 ), first electrode ( 4 ) disposed in he vacuum chamber ( 3 ), and a second electrode ( 5 ) disposed upstream of the first electrode ( 4 ) in the vacuum chamber ( 3 ). The beam processing apparatus further comprises a voltage applying unit for applying a variable voltage between the first electrode ( 4 ) and the second electrode ( 5 ) to alternately extract positive ions ( 6 ) and negative ions from the plasma generated by the plasma generator.

BACKGROUND ART

[0001] The present invention relates to a beam processing apparatus, andmore particularly to a beam processing apparatus for generating a highlydirectional and highly dense particle beam from a high-density plasmaand processing a workpiece with the generated particle beam.

TECHNICAL FIELD

[0002] In recent years, semiconductor integrated circuits, informationstorage media such as hard disks, micromachines, and the like have beenprocessed in highly fine patterns. In the fields of processing suchworkpieces, attention has been attracted to the use of an energetic beamsuch as a high-density ion beam which is highly linear, i.e., highlydirectional, and has a relatively large beam diameter. For example, theenergetic beam is applied to a workpiece for depositing a film thereonor etching the workpiece.

[0003] As beam sources of such energetic beams, there have been usedbeam generators which generate various kinds of beams including apositive ion beam, a negative ion beam, and a radical beam. The positiveion beam, the negative ion beam, or the radical beam is applied to adesired area of a workpiece from the beam source, for thereby locallydepositing a film on the workpiece, etching the workpiece, modifying thesurface of the workpiece, or joining or bonding parts of the workpiece.

[0004] In the case of a beam source which applies charged particles suchas positive ions or negative ions to a workpiece, an insulated workpiececannot be processed because of a charge build-up phenomenon in whichelectric charges are built up on the workpiece. Further, since the ionbeam emitted from the beam source tends to spread due to thespace-charge effect, the workpiece cannot be processed in a finepattern.

[0005] In order to solve the above problems, there has been proposed amethod of introducing electrons into the ion beam to neutralize theelectric charges. This method can balance the electric charges on theworkpiece on the whole. However, since local unbalance of the electriccharges still remains on the workpiece, the workpiece cannot beprocessed in a fine pattern.

[0006] In the case where ions are extracted from a plasma source andapplied to a workpiece, if a radiation (e.g., an ultraviolet ray)produced by the plasma source is applied to the workpiece, then theradiation adversely affects the workpiece. Thus, it is necessary toshield the workpiece from an adverse radiation (e.g., an ultravioletray) emitted from the plasma source.

DISCLOSURE OF INVENTION

[0007] The present invention has been made in view of the abovedrawbacks. It is therefore an object of the present invention to providea beam processing apparatus which can apply an energetic beam having alarge beam diameter to a workpiece with an inexpensive and compactstructure, and can neutralize ions with a high neutralization efficiencyto process the workpiece without a charge build-up or damage.

[0008] According to a first aspect of the present invention, there isprovided a beam processing apparatus comprising: a workpiece holder forholding a workpiece; a plasma generator for generating a plasma in avacuum chamber; a first electrode disposed in the vacuum chamber; asecond electrode disposed upstream of the fist electrode in the vacuumchamber; and a voltage applying unit for applying a variable voltagebetween the first electrode and the second electrode to alternatelyextract positive ions and negative ions from the plasma generated by theplasma generator.

[0009] With the above arrangement, positive ions and negative ions canalternately be extracted from a plasma. The extracted positive andnegative ions are neutralized and applied as a neutral particle beam tothe workpiece, or directly applied as a positive ion beam and a negativeion beam to the workpiece.

[0010] The plasma generator may generate the plasma by applying ahigh-frequency electric field. The beam processing apparatus may furthercomprise a negative ion generating chamber disposed downstream of theplasma generator for attaching electrons to a residual gas to generatenegative ions therein. The negative ion generating chamber may have anelectron cloud generator for generating an electron cloud within thenegative ion generating chamber.

[0011] According to a second aspect of the present invention, there isprovided a beam processing apparatus comprising: a workpiece holder forholding a workpiece; a first electrode disposed in a vacuum chamber; asecond electrode disposed upstream of the fist electrode in the vacuumchamber; and a voltage applying unit for applying a variable voltagebetween the first electrode and the second electrode to generate aplasma between the first electrode and the second electrode and toalternately extract positive ions and negative ions from the generatedplasma.

[0012] With the above arrangement, positive ions and negative ions canalternately be extracted from a plasma. The extracted positive andnegative ions are neutralized and applied as a neutral particle beam tothe workpiece, or directly applied as a positive ion beam and a negativeion beam to the workpiece. Particularly, the voltage applying unitserves not only to extract the positive ions and the negative ions, butalso to generate the plasma. Therefore, it is not necessary to provide aseparate plasma generator for generating a plasma. Thus, the beamprocessing apparatus can be made compact in structure, and a beamdiameter of an energetic beam can be increased inexpensively.

[0013] According to a preferred aspect of the present invention, thebeam processing apparatus further comprises a neutralization device foralternately neutralizing the positive ions and the negative ionsextracted by the voltage applying unit.

[0014] With the above arrangement, positive ions and negative ions canalternately be extracted from a plasma. The extracted positive andnegative ions are neutralized and applied as a neutral particle beam tothe workpiece. Since the workpiece can be processed by the neutralparticle beam having no electric charges but having a largetranslational energy, various processes including an etching process anda deposition process can be performed on the workpiece with highaccuracy in such a state that an amount of charge build-up is reduced.Further, the neutral particles generated by neutralization of thepositive ions and the neutral particles generated by neutralization ofthe negative ions are alternately applied to the workpiece. Therefore,two types of processes are alternately performed on the workpiece. Forexample, when gases of Cl₂ and Xe are introduced into the vacuumchamber, the workpiece is sputtered with use of Xe generated byneutralization of the positive ions and etched with use of chlorinegenerated by neutralization of the negative ions. In this case, theetching rate can be enhanced by chemical sputtering effect. For example,a chlorine beam is applied to a workpiece to form thereon several atomiclayers in which the chlorine and the workpiece are weakly bonded to eachother, and then a Xe beam is applied to the workpiece. When the energyof the Xe beam is larger than the energy required for removing theatomic layers in which the chlorine and the workpiece are weakly bondedto each other, but is smaller than the energy required for removing theatomic layers in the workpiece which have a large bonding strength, theXe beam can sputter the workpiece to remove only the atomic layers inwhich the chlorine and the workpiece are weakly bonded to each other.Thus, when reaction processes are properly selected and the energy of abeam is properly controlled, a workpiece can be etched without defect ofthe crystal structure of atoms in the workpiece.

[0015] It is desirable that the neutralization device has an orificeelectrode as the first electrode and a grid electrode as the secondelectrode, and the voltage applying unit applies a variable voltagebetween the orifice electrode and the grid electrode to alternatelyextract positive ions and negative ions from the plasma and toalternately pass the positive ions and the negative ions throughorifices defined in the orifice electrode.

[0016] With the above arrangement, the voltage applying unit serves notonly to extract the positive ions and the negative ions, but also toneutralize the ions. When the orifice electrode is used for neutralizingthe positive ions and the negative ions, a high neutralizationefficiency can be obtained, and hence a beam diameter of an energeticbeam can be increased inexpensively without increasing the size of theapparatus. Further, since the generated plasma is isolated from theworkpiece by the orifice electrode, a radiation produced by the plasmais not substantially applied to the workpiece. Therefore, it is possibleto reduce adverse effects on the workpiece due to the radiation such asan ultraviolet ray which would otherwise damage the workpiece.

[0017] The above and other objects, features, and advantages of thepresent invention will be apparent from the following description whentaken in conjunction with the accompanying drawings which illustratespreferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF DRAWINGS

[0018]FIG. 1 is a schematic view showing a whole arrangement of a beamprocessing apparatus according to a first embodiment of the presentinvention;

[0019]FIG. 2A is a perspective view showing an orifice electrode and agrid electrode in the beam processing apparatus shown in FIG. 1;

[0020]FIG. 2B is a vertical cross-sectional view partially showing theorifice electrode and the grid electrode shown in FIG. 2A, in whichpositive ions are being neutralized;

[0021]FIG. 3 is a timing chart showing operating states of the beamprocessing apparatus shown in FIG. 1;

[0022]FIG. 4 is a schematic view showing a whole arrangement of a beamprocessing apparatus according to a modification of the first embodimentof the present invention;

[0023]FIG. 5 is a schematic view showing a whole arrangement of a beamprocessing apparatus according to a second embodiment of the presentinvention;

[0024]FIG. 6 is a timing chart showing operating states of the beamprocessing apparatus shown in FIG. 5;

[0025]FIG. 7 is a schematic view showing a whole arrangement of a beamprocessing apparatus according to a third embodiment of the presentinvention;

[0026]FIG. 8 is a cross-sectional view showing an electron cloudgenerator in the beam processing apparatus shown in FIG. 7;

[0027]FIG. 9 is a timing chart showing operating states of the beamprocessing apparatus shown in FIG. 7;

[0028]FIG. 10 is a schematic view showing a whole arrangement of a beamprocessing apparatus according to a modification of the third embodimentof the present invention;

[0029]FIG. 11 is a schematic view showing a whole arrangement in whichpositive ions and negative ions are alternately applied to a workpiecewithout being neutralized in the beam processing apparatus of the firstembodiment;

[0030]FIG. 12 is a schematic view showing a whole arrangement in whichpositive ions and negative ions are alternately applied to a workpiecewithout being neutralized in the beam processing apparatus shown in FIG.4;

[0031]FIG. 13 is a schematic view showing a whole arrangement in whichpositive ions and negative ions are alternately applied to a workpiecewithout being neutralized in the beam processing apparatus of the thirdembodiment;

[0032]FIG. 14 is a schematic view showing a whole arrangement in whichpositive ions and negative ions are alternately applied to a workpiecewithout being neutralized in the beam processing apparatus shown in FIG.10; and

[0033]FIG. 15 is a timing chart showing an example of a voltage to beapplied instead of a low-frequency voltage.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] A beam processing apparatus according to a first embodiment ofthe present invention will be described in detail below with referenceto FIGS. 1 through 3.

[0035]FIG. 1 is a schematic view showing a whole arrangement of a beamprocessing apparatus according to a first embodiment of the presentinvention, with electric components in block form. As shown in FIG. 1,the beam processing apparatus comprises a cylindrical vacuum chamber 3constituted by a beam generating chamber 1 for generating a neutralparticle beam and a process chamber 2 for processing a workpiece X suchas a semiconductor substrate, a glass workpiece, an organic workpiece, aceramic workpiece, or the like. The beam generating chamber 1 of thevacuum chamber 3 has walls made of quartz glass or ceramics, and theprocess chamber 2 of the vacuum chamber 3 has walls made of metal.

[0036] The beam generating chamber 1 has a coil 10 disposed therearoundfor inductively coupled plasma (ICP). The coil 10 is housed in awater-cooled tube having an outside diameter of 8 mm, for example. Thecoil 10 of about two turns is wound around the beam generating chamber1. The coil 10 is electrically connected through a matching box 100 to ahigh-frequency power supply 101, which applies a high-frequency voltagehaving a frequency of about 13.56 MHz, for example, to the coil 10. Whena high-frequency current is supplied from the high-frequency powersupply 101 via the matching box 100 to the coil 10, an induced magneticfield is produced in the beam generating chamber 1 by the coil 10. Thevarying magnetic field induces an electric field, which accelerateselectrons to generate a plasma in the beam generating chamber 1. Thus,the coil 10, the matching box 100, and the high-frequency power supply101 constitute a plasma generator for generating a plasma in the beamgenerating chamber 1.

[0037] The beam generating chamber 1 has a gas inlet port 11 defined inan upper portion thereof for introducing a gas into the beam generatingchamber 1. The gas inlet port 11 is connected through a gas supply pipe12 to a gas supply source 13, which supplies a gas such as SF₆, CHF₃,CF₄, Cl₂, Ar, O₂, N₂, and C₄F₈ to the beam generating chamber 1.

[0038] The process chamber 2 houses a workpiece holder 20 therein forholding a workpiece X. The workpiece X is placed on an upper surface ofthe workpiece holder 20. The process chamber 2 has a gas outlet port 21defined in a sidewall thereof for discharging the gas from the processchamber 2. The gas outlet port 21 is connected through a gas outlet pipe22 to a vacuum pump 23, which operates to maintain the process chamber 2at a predetermined pressure.

[0039] An orifice plate (orifice electrode) 4 made of an electricallyconductive material such as graphite is disposed in the lower end of thebeam generating chamber 1 and electrically grounded. The orificeelectrode 4 serves as a first electrode and also serves to neutralizeions. A thin-plate grid electrode (second electrode) 5 made of anelectrically conductive material is disposed above the orifice electrode4. The grid electrode 5 is electrically connected to a bipolar powersupply (voltage applying unit) 102, which applies a low-frequencyvoltage having a frequency of about 400 kHz, for example, to the gridelectrode 5.

[0040]FIG. 2A is a perspective view showing the orifice electrode 4 andthe grid electrode 5, and FIG. 2B is a vertical cross-sectional viewpartially showing the orifice electrode 4 and the grid electrode 5 shownin FIG. 2A. As shown in FIGS. 2A and 2B, the orifice electrode 4 has anumber of orifices 4 a defined therein, and the grid electrode 5 has anumber of grid holes 5 a defined therein. The grid electrode 5 maycomprise a meshed wire, a punching metal, or the like.

[0041] The high-frequency power supply 101 which is connected to thecoil 10 is connected a modulator 103, and the bipolar power supply 102which is connected to the grid electrode 5 is connected to a modulator104. Thus, the high-frequency power supply 101 and the bipolar powersupply 102 are connected to each other through the modulators 103, 104.The application of the voltage by the bipolar power supply 102 issynchronized with the application of the voltage by the high-frequencypower supply 101, based on synchronizing signals transmitted between themodulators 103, 104.

[0042] Operation of the beam processing apparatus according to the firstembodiment will be described below. FIG. 3 is a timing chart showingoperating states of the beam processing apparatus shown in FIG. 1. InFIG. 3, Va represents the potential of the coil 10, Te the electrontemperature in the beam generating chamber 1, ne the electron density inthe beam generating chamber 1, ni⁻ the negative ion density in the beamgenerating chamber 1, and Vb the potential of the grid electrode 5. Thetiming chart is schematically shown in FIG. 3, and the shown frequenciesare different from the actual frequencies, for example.

[0043] The vacuum pump 23 is driven to evacuate the vacuum chamber 3,and then a gas such as SF₆, CHF₃, CF₄, Cl₂, Ar, O₂, N₂, or C₄F₈ isintroduced from the gas supply source 13 into the beam generatingchamber 1. As shown in FIG. 3, a high-frequency voltage having afrequency of about 13.56 MHz is applied to the coil 10 for 10microseconds by the high-frequency power supply 101, so that ahigh-frequency electric field is produced in the beam generating chamber1. The gas introduced into the beam generating chamber 1 is ionized byelectrons that are accelerated by the high-frequency electric field, forthereby generating a high-density plasma in the beam generating chamber1. The plasma is mainly composed of positive ions and heated electrons.

[0044] Then, the high-frequency voltage applied by the high-frequencypower supply 101 is interrupted for 100 microseconds. Thereafter, thehigh-frequency voltage is applied again to the coil 10 for 10microseconds by the high-frequency power supply 101 to heat theelectrons in the plasma in the beam generating chamber 1. Thus, theabove cycle is repeated. In this manner, the application of thehigh-frequency voltage for 10 microseconds and the interruption of thehigh-frequency voltage for 100 microseconds are alternately repeated.The period of time (100 microseconds) for which the high-frequencyvoltage is interrupted is sufficiently longer than a period of time inwhich the electrons in the plasma are attached to the residual processgas to generate negative ions, and sufficiently shorter than a period oftime in which the electron density in the plasma is lowered toextinguish the plasma. The period of time (10 microseconds) for whichthe high-frequency voltage is applied is long enough to recover theenergy of the electrons in the plasma which has been lowered during theinterruption of the high-frequency voltage.

[0045] Negative ions can be generated efficiently and continuously byinterrupting the high-frequency voltage after the energy of theelectrons is increased in the plasma. While ordinary plasmas are mostlycomposed of positive ions and electrons, the beam processing apparatusaccording to the present embodiment can efficiently generate a plasma inwhich positive ions and negative ions coexist therein. Although thehigh-frequency voltage is interrupted for 100 microseconds in the aboveexample, it may be interrupted for a period of time ranging from 50 to100 microseconds to generate a large quantity of negative ions as wellas positive ions in the plasma.

[0046] After 50 microseconds from the time when the high-frequencyvoltage applied by the high-frequency power supply 101 is stopped, alow-frequency voltage having a frequency of about 400 kHz is applied tothe grid electrode 5 for 50 microseconds by the bipolar power supply102. In the application of the low-frequency voltage, when the potentialVb of the grid electrode is higher than the potential (ground potential)of the orifice electrode 4 (for example, during a period “A” illustratedin FIG. 3), a potential difference is produced between the orificeelectrode 4 and the grid electrode 5 so that orifice electrode 4 servesas a cathode and the grid electrode 5 serves as an anode. Therefore, thepositive ions 6 (see FIG. 2B) that have passed through the gridelectrode 5 toward the orifice electrode 4 are accelerated toward theorifice electrode 4 by the potential difference and introduced into theorifices 4 a defined in the orifice electrode 4.

[0047] Most of the positive ions 6 that are passing through the orifices4 a in the orifice electrode 4 are collided with the sidewall surfacesof the orifices 4 a and hence neutralized in the vicinity of solidsidewall surfaces of the orifices 4 a, or are collided with gasmolecules remaining within the orifices 4 a and hence neutralized bycharge exchange with the gas molecules, or are collided with electronsemitted from the surface of the orifice electrode 4 and henceneutralized by recombination with the electrons. Thus, the positive ions6 are converted into neutral particles 7 (see FIG. 2B).

[0048] When the potential Vb of the grid electrode is lower than thepotential (ground potential) of the orifice electrode 4 (for example,during a period “B” illustrated in FIG. 3), a potential difference isproduced between the orifice electrode 4 and the grid electrode 5 sothat orifice electrode 4 serves as an anode and the grid electrode 5serves as a cathode. Therefore, the negative ions that have passedthrough the grid electrode 5 toward the orifice electrode 4 areaccelerated toward the orifice electrode 4 by the potential differenceand introduced into the orifices 4 a defined in the orifice electrode 4.Most of the negative ions 6 that are passing through the orifices 4 a inthe orifice electrode 4 are collided with the sidewall surfaces of theorifices 4 a and hence neutralized in the vicinity of solid sidewallsurfaces of the orifices 4 a, or are collided with gas moleculesremaining within the orifices 4 a and hence neutralized by chargeexchange with the gas molecules. Thus, the negative ions are convertedinto neutral particles 7.

[0049] Thus, the negative and positive ions that have been neutralizedwhen passing through the orifices 4 a, i.e., the neutral particles, arethen emitted as an energetic beam into the process chamber 2. Theneutral particles 7 travel directly in the process chamber 2 and areapplied to the workpiece X placed on the workpiece holder 20, forthereby etching the surface of the workpiece X, cleaning the surface ofthe workpiece X, modifying (e.g., nitriding or oxidizing) the surface ofthe workpiece X, or depositing a film on the workpiece X.

[0050] As described above, the neutral particles generated byneutralization of the positive ions and the neutral particles generatedby neutralization of the negative ions are alternately applied to theworkpiece. Therefore, two types of processes are alternately performedon the workpiece. For example, when gases of Cl₂ and Xe are introducedinto the beam generating chamber 1, the workpiece is sputtered with useof Xe generated by neutralization of the positive ions and etched withuse of chlorine generated by neutralization of the negative ions. Inthis case, the etching rate can be enhanced by chemical sputteringeffect.

[0051] For example, a chlorine beam is applied to a workpiece to formthereon several atomic layers in which the chlorine and the workpieceare weakly bonded to each other, and then a Xe beam is applied to theworkpiece. When the energy of the Xe beam is larger than the energyrequired for removing the atomic layers in which the chlorine and theworkpiece are weakly bonded to each other, but is smaller than theenergy required for removing the atomic layers in the workpiece whichhave a large bonding strength, the Xe beam can sputter the workpiece toremove only the atomic layers in which the chlorine and the workpieceare weakly bonded to each other. Thus, when reaction processes areproperly selected and the energy of a beam is properly controlled, aworkpiece can be etched without destruction of the crystal structure ofatoms in the workpiece.

[0052] The orifice electrode 4 serves not only to neutralize the ions,but also to prevent a radiation produced by the plasma from beingapplied to the workpiece X. Specifically, since the beam generatingchamber 1 where the plasma is generated is isolated from the workpiece Xby the orifice electrode 4, the radiation produced by the plasma is notsubstantially applied to the workpiece X. Therefore, it is possible toreduce adverse effects on the workpiece X due to the radiation such asan ultraviolet ray which would otherwise damage the workpiece X.

[0053] Some charged particles may pass through the orifices 4 a in theorifice electrode 4. In order to prevent such charged particles frombeing applied to the workpiece X, a deflector or an electron trap may bedisposed downstream of the orifice electrode 4. A voltage is applied tothe deflector in a direction perpendicular to a beam traveling directionto change the traveling direction of charged particles, for therebypreventing the charged particles from being applied to the workpiece X.The electron trap produces a magnetic field of about 100 gauss in adirection perpendicular to a beam traveling direction to change thetraveling direction of electrons, for thereby preventing the electronsfrom being applied to the workpiece X.

[0054] As well known in the art, when an insulated workpiece such as aworkpiece made of glass or ceramics is processed, charge build-up may bedeveloped on the surface of the insulated workpiece. However, byapplying neutralized particles to the insulating workpiece as describedabove, various processes including an etching process and a depositionprocess can be performed on the insulating workpiece with high accuracyin such a state that an amount of charge build-up is reduced. Varioustypes of gases may be introduced into the beam generating chamber 1according to the type of process to be performed on the workpiece X. Forexample, in a dry etching process, oxygen or a halogen gas mayselectively be used according to the kind of the workpiece X.

[0055] In the first embodiment, the grid electrode 5 is positioneddownstream of the coil 10. However, the grid electrode may be positionedupstream of the coil 10. In such a case, the grid electrode may have nogrid holes therein. FIG. 4 is a schematic view showing a wholearrangement of a beam processing apparatus where a grid electrode 50 isdisposed upstream of the coil 10. In the beam processing apparatus shownin FIG. 4, negative ions in a plasma generated in the beam generatingchamber 1 are accelerated by a voltage applied between the gridelectrode 50 and the orifice electrode 4.

[0056] In the first embodiment, the orifice electrode and the gridelectrode are used as a neutralization device for neutralizing ions.However, the neutralization device is not limited to the illustratedexample. The present invention is also applicable to neutralizationdevices which perform the following processes, for example.

[0057] 1) An electron beam is applied to ions extracted from a plasma toneutralize the ions.

[0058] 2) A neutral gas is introduced into a path of ions extracted froma plasma to form a region of the neutral gas having a high pressure, andthe ions are passed through this region for neutralization.

[0059] 3) A light is applied to ions to neutralize the ions.

[0060] 4) Ions are be vibrated by a high-frequency electric field forneutralization.

[0061] 5) A electron cloud is formed in a path of ions extracted from aplasma, and the ions are passed through the electron cloud forneutralization.

[0062] A beam processing apparatus according to a second embodiment ofthe present invention will be described below with reference to FIGS. 5and 6. FIG. 5 is a schematic view showing a whole arrangement of a beamprocessing apparatus according to a second embodiment of the presentinvention, with electric components in block form. In FIG. 5, like partsand components are denoted by the same reference numerals and charactersas those of the first embodiment and will not be described below.

[0063] In the present embodiment, the beam processing apparatuscomprises a vacuum chamber 30 made of metal, i.e., a metallic chamber.As shown in FIG. 5, a thin-plate grid electrode (second electrode) 8made of an electrically conductive material is disposed in an upstreamend of the vacuum chamber 30. The vacuum chamber 30 and the gridelectrode 8 are electrically connected to each other and electricallygrounded.

[0064] An AC power supply 105 and an AC power supply 106, which areconnected parallel to each other, are electrically connected to theorifice electrode (a first electrode) 4. The power supplies 105, 106 arealso connected to modulators 107, 108, respectively. The modulator 107for the AC power supply 105 and the modulator 108 for the AC powersupply 106 are synchronized with each other by synchronizing signals. Avoltage applying unit is constituted by the AC power supplies 105, 106,and the modulators 107, 108. The vacuum chamber 30 and the orificeelectrode 4 are electrically insulated from each other by an insulatingmaterial (not shown). The surfaces of the orifice electrode 4 may becovered with dielectric films.

[0065] Operation of the beam processing apparatus according to thesecond embodiment will be described below. FIG. 6 is a timing chartshowing operating states of the beam processing apparatus shown in FIG.5. In FIG. 6, Vc represents the potential of the AC power supply 105, Tethe electron temperature in the beam generating chamber 1, ne theelectron density in the beam generating chamber 1, ni⁻ the negative iondensity in the beam generating chamber 1, Vd the potential of the ACpower supply 106, and Ve the potential of the orifice electrode 4. Thetiming chart is schematically shown in FIG. 6, and the shown frequenciesare different from the actual frequencies, for example.

[0066] The vacuum pump 23 is driven to evacuate the vacuum chamber 30,and then a gas is introduced from the gas supply source 13 into the beamgenerating chamber 1. As shown in FIG. 6, a high-frequency voltagehaving a frequency of about 13.56 MHz is applied to the orificeelectrode 4 for 10 microseconds by the AC power supply 105, so that ahigh-frequency electric field is produced in the beam generating chamber1. The gas introduced into the beam generating chamber 1 is ionized byelectrons that are accelerated by the high-frequency electric field, forthereby generating a high-density plasma in the beam generating chamber1.

[0067] Then, the high-frequency voltage applied by the AC power supply105 is interrupted for 100 microseconds. Thereafter, the high-frequencyvoltage is applied again to the orifice electrode 4 for 10 microsecondsby the AC power supply 105 to heat the electrons in the plasma in thebeam generating chamber 1. Thus, the above cycle is repeated. In thismanner, the application of the high-frequency voltage for 10microseconds and the interruption of the high-frequency voltage for 100microseconds are alternately repeated.

[0068] Negative ions can be generated efficiently and continuously byinterrupting the high-frequency voltage after the energy of theelectrons is increased in the plasma. While ordinary plasmas are mostlycomposed of positive ions and electrons, the beam processing apparatusaccording to the present embodiment can efficiently generate a plasma inwhich positive ions and negative ions coexist therein.

[0069] After 50 microseconds from the time when the high-frequencyvoltage applied by the AC power supply 105 is stopped, a low-frequencyvoltage having a frequency of 400 kHz is applied to the orificeelectrode 4 for 50 microseconds by the AC power supply 106. As in thecase of the first embodiment, positive and negative ions are alternatelyaccelerated toward the orifice electrode 4 by the potential differencesproduced by the low-frequency voltage, and introduced into the orifices4 a defined in the orifice electrode 4.

[0070] Most of the positive and negative ions that are passing throughthe orifices 4 a are alternately neutralized and converted into neutralparticles as in the case of the first embodiment. The neutral particlesare then emitted as an energetic beam into the process chamber 2. Theneutral particles travel directly in the process chamber 2 and areapplied to the workpiece X placed on the workpiece holder 20.

[0071] According to the second embodiment, as described above, byalternately applying the high-frequency voltage and the low-frequencyvoltage between the orifice electrode 4 and the grid electrode 8, aplasma can be generated in the beam generating chamber, and negativeions can be extracted from the generated plasma. Therefore, it is notnecessary to provide a separate plasma generator for generating aplasma. Thus, the beam processing apparatus can be made compact instructure, and a beam diameter of an energetic beam can be increasedinexpensively.

[0072] A beam processing apparatus according to a third embodiment ofthe present invention will be described below with reference to FIGS. 7through 9. FIG. 7 is a schematic view showing a whole arrangement of abeam processing apparatus according to a third embodiment of the presentinvention, with electric components in block form. In FIG. 7, like partsand components are denoted by the same reference numerals and charactersas those of the first embodiment and will not be described below.

[0073] The present embodiment differs from the first embodiment in thata beam generating chamber 31 has a negative ion generating chamber 31 aformed downstream of a coil 10 for attaching electrons to a residual gasto generate negative ions. Thus, the beam processing apparatus in thepresent embodiment comprises a downstream beam processing apparatushaving a negative ion generating chamber formed downstream of agenerated plasma.

[0074] The negative ion generating chamber 31 a may have an electroncloud generator for generating an electron cloud within the negative iongenerating chamber 31 a as needed. Specifically, permanent magnets 9 aredisposed around the negative ion generating chamber 31 a atpredetermined circumferential intervals, as shown in FIG. 8. Thepermanent magnets 9 are arranged so that the magnetic poles of theadjacent permanent magnets are opposed to each other. With thisarrangement, the permanent magnets 9 produce a magnetic field in thenegative ion generating chamber 31 a, and electrons in the plasma movealong an orbital path C shown in FIG. 8 to form an electron cloud in thenegative ion generating chamber 31 a. In the present embodiment, theelectron cloud generator utilizes the permanent magnets 9. However, theelectron cloud generator may utilize an electric field applied in thenegative ion generating chamber 31.

[0075] The grid electrode 5 is electrically connected to a low-frequencypower supply 109, which applies a low-frequency voltage having afrequency of about 400 kHz, for example, to the grid electrode 5. In thepresent embodiment, the beam processing apparatus has no modulators,unlike the first embodiment.

[0076] Operation of the beam processing apparatus according to the thirdembodiment will be described below. FIG. 9 is a timing chart showingoperating states of the beam processing apparatus shown in FIG. 7. InFIG. 9, Vf represents the potential of the coil 10, and Vg representsthe potential of the grid electrode 5. The timing chart is schematicallyshown in FIG. 9, and the shown frequencies are different from the actualfrequencies, for example.

[0077] The vacuum pump 23 is driven to evacuate the vacuum chamber 3,and then a gas such as SF₆, CHF₃, CF₄, Cl₂, Ar, O₂, or C₄F₈ isintroduced from the gas supply source 13 into the beam generatingchamber 31. As shown in FIG. 9, a high-frequency voltage having afrequency of about 13.56 MHz is applied to the coil 10 for 10microseconds by the high-frequency power supply 101, so that ahigh-frequency electric field is produced in the beam generating chamber31. The gas introduced into the beam generating chamber 31 is ionized byelectrons that are accelerated by the high-frequency electric field, forthereby generating a high-density plasma in the beam generating chamber31. The plasma is mainly composed of positive ions and heated electrons.

[0078] As described above, in the present embodiment, the negative iongenerating chamber 31 a is provided downstream of the plasma. In thenegative ion generating chamber 31 a, electrons lowered in electrontemperature are attached to the residual gas to generate negative ions.Therefore, positive ions, negative ions, and electrons are present inthe negative ion generating chamber 31 a.

[0079] At the same time when the high-frequency voltage is applied bythe high-frequency power supply 101, a low-frequency voltage having afrequency of about 400 kHz is applied between the grid electrode 5 andthe orifice electrode 4 by the low-frequency power supply 109. As in thecase of the first embodiment, positive and negative ions are alternatelyaccelerated toward the orifice electrode 4 by the potential differencesproduced by the low-frequency voltage, and introduced into the orifices4 a defined in the orifice electrode 4.

[0080] Most of the positive and negative ions that are passing throughthe orifices 4 a are alternately neutralized and converted into neutralparticles as in the case of the first embodiment. The neutral particlesare then emitted as an energetic beam into the process chamber 2. Theneutral particles travel directly in the process chamber 2 and areapplied to the workpiece X placed on the workpiece holder 20.

[0081] The grid electrode may be positioned upstream of the coil 10.FIG. 10 is a schematic view showing a whole arrangement of a beamprocessing apparatus where a grid electrode 50 is disposed upstream ofthe coil 10. In the beam processing apparatus shown in FIG. 10, positiveand negative ions in a plasma generated in the beam generating chamber 1are accelerated by a voltage applied between the grid electrode 50 andthe orifice electrode 4.

[0082] In the above embodiments, positive ions and negative ions arealternately extracted from a plasma and neutralized. However, positiveions and negative ions may alternately be extracted from a plasma anddirectly applied as a positive ion beam and a negative ion beam to aworkpiece without being neutralized.

[0083]FIG. 11 is a schematic view showing a whole arrangement in whichpositive ions and negative ions are alternately applied as a positiveion beam and a negative ion beam to a workpiece X without beingneutralized in the beam processing apparatus of the first embodiment. InFIG. 11, a thin-plate grid electrode (second electrode) 51 made of anelectrically conductive material is disposed instead of the orificeelectrode. The grid electrode 51 is electrically grounded as in the caseof the orifice electrode in the first embodiment. With this arrangement,a high-frequency voltage is applied to a coil 10 for 10 microseconds bythe high-frequency power supply 101 to generate a high-density plasma inthe beam generating chamber 1. After 50 microseconds from the time whenthe high-frequency voltage applied by the high-frequency power supply101 is stopped, a low-frequency voltage is applied to the grid electrode5 for 50 microseconds by the bipolar power supply 102. As in the case ofthe first embodiment, positive ions and negative ions are alternatelyemitted from the grid electrode 51 and applied as a positive ion beamand a negative ion beam to the workpiece X.

[0084] In the embodiment shown in FIG. 4, the third embodiment, and theembodiment shown in FIG. 10, positive ions and negative ions may bealternately applied to the workpiece X without being neutralized. FIGS.12 through 14 are schematic views showing a whole arrangement in suchcases. FIG. 12 corresponds to the embodiment shown in FIG. 4, FIG. 13the third embodiment, and FIG. 14 the embodiment shown in FIG. 10.

[0085] In the above embodiments, the plasma is generated with use of acoil for ICP. However, the plasma may be generated with use of anelectron cyclotron resonance source (ECR source), a coil for heliconwave plasma, a microwave, or the like. The frequency of thehigh-frequency voltage is not limited to 13.56 MHz, but may be in therange from 1 MHz to 20 GHz. Further, the frequency of the low-frequencyvoltage is not limited to 400 kHz. For example, a voltage of arectangular wave as shown in FIG. 15 may be applied instead of thelow-frequency voltage.

[0086] Although certain preferred embodiments of the present inventionhave been shown and described in detail, it should be understood thatvarious changes and modifications may be made therein without departingfrom the scope of the appended claims.

INDUSTRIAL APPLICABILITY

[0087] The present invention is suitable for use in a beam processingapparatus for generating a highly directional and highly dense particlebeam from a high-density plasma and processing a workpiece with thegenerated particle beam.

1. A beam processing apparatus comprising: a workpiece holder forholding a workpiece; a plasma generator for generating a plasma in avacuum chamber; a first electrode disposed in said vacuum chamber; asecond electrode disposed upstream of said fist electrode in said vacuumchamber; and a voltage applying unit for applying a variable voltagebetween said first electrode and said second electrode to alternatelyextract positive ions and negative ions from the plasma generated bysaid plasma generator.
 2. A beam processing apparatus according to claim1, wherein said plasma generator generates said plasma by applying ahigh-frequency electric field.
 3. A beam processing apparatus accordingto claim 1, further comprising a negative ion generating chamberdisposed downstream of said plasma generator for attaching electrons toa residual gas to generate negative ions therein.
 4. A beam processingapparatus according to claim 3, wherein said negative ion generatingchamber has an electron cloud generator for generating an electron cloudwithin said negative ion generating chamber.
 5. A beam processingapparatus according to claim 1, further comprising a neutralizationdevice for alternately neutralizing said positive ions and said negativeions extracted by said voltage applying unit.
 6. A beam processingapparatus according to claim 5, wherein said neutralization device hasan orifice electrode as said first electrode and a grid electrode assaid second electrode; and said voltage applying unit applies a variablevoltage between said orifice electrode and said grid electrode toalternately extract positive ions and negative ions from said plasma andto alternately pass said positive ions and said negative ions throughorifices defined in said orifice electrode.
 7. A beam processingapparatus comprising: a workpiece holder for holding a workpiece; afirst electrode disposed in a vacuum chamber; a second electrodedisposed upstream of said fist electrode in said vacuum chamber; and avoltage applying unit for applying a variable voltage between said firstelectrode and said second electrode to generate a plasma between saidfirst electrode and said second electrode and to alternately extractpositive ions and negative ions from the generated plasma.
 8. A beamprocessing apparatus according to claim 7, further comprising aneutralization device for alternately neutralizing said positive ionsand said negative ions extracted by said voltage applying unit.
 9. Abeam processing apparatus according to claim 8, wherein saidneutralization device has an orifice electrode as said first electrodeand a grid electrode as said second electrode; and said voltage applyingunit applies a variable voltage between said orifice electrode and saidgrid electrode to alternately extract positive ions and negative ionsfrom said plasma and to alternately pass said positive ions and saidnegative ions through orifices defined in said orifice electrode.